Aqueous electrodeposition paints and the production and use thereof

ABSTRACT

Aqueous electrophoretic lacquer capable of being deposited cataphoretically, containing
     A) an aqueous dispersion of cationically modified polyurethane (meth)acrylates (a1) with terminal, ethylenically unsaturated (meth)acrylic double bonds, and reactive thinner (a2) with at least two ethylenically unsaturated (meth)acrylic double bonds, the (meth)acrylic double bonds of the mixture of (a1) and (a2) corresponding to a bromine number of 20 to 150 g bromine/100 g solids, and   B) photoinitiators and optionally free-radical initiators capable of thermal activation,
       the terminal, ethylenically unsaturated (meth)acrylic double bonds of the polyurethane (meth)acrylates being bonded with the anionically modified polyurethane prepolymer via urethane, urea, amide or ester groups,   and optionally conventional auxiliary substances and additives, pigments and/or fillers.

BACKGROUND OF THE INVENTION

The invention relates to aqueous electrophoretic lacquers capable ofbeing deposited cataphoretically, which are curable by high-energyradiation and have the advantage of a good full cure even with high filmthicknesses, and give good mechanical properties and, in particular,high resistance in an industrial gas atmosphere. It also relates totheir production and use for the lacquering of electrically conductivesubstrates, e.g. of metal, electrically conductive plastic, e.g.metallised plastic, or electrically conductive coatings.

Coatings applied by the electrophoretic lacquer process have theadvantage that they contain only a small quantity of residual water. Thecoating obtained does not therefore have to be pre-dried after rinsingoff any bath material still adhering, but can be cured by high-energyradiation after possibly blowing off droplets of water.

In U.S. Pat. No. 4,039,414, compositions for the electrophoretic lacquerprocess are described containing a photoinitiator, dispersed in anethylenically unsaturated polymer, dispersed in an aqueous phase, whichcan be deposited at a cathode and cured with TV radiation. In general, anumber of acrylated polymers are mentioned, among which, as the onlypolyurethane acrylate, one that uses toluylene diisocyanate andpolyether polyols as structural components is described. Lacquers onthis basis have a tendency towards severe yellowing and towards earlysigns of degradation caused by weathering, leading to cracking,reduction in gloss and chalking, and also prove relatively brittle.

The invention was therefore based on the object of providing aqueouselectrophoretic lacquers capable of being deposited cataphoretically,which do not exhibit these defects, which cure fully by high-energyradiation, even in high film thicknesses, and give lacquer films withimproved properties compared with the prior art, particularly withregard to resistance in an industrial gas atmosphere, improvedflexibility and good adhesion to the substrate.

SUMMARY OF THE INVENTION

It has been shown that this object can be achieved with the aqueouselectrophoretic lacquer capable of being deposited cataphoreticallyprovided by the invention, which contains

-   A) an aqueous dispersion containing one or more cationically    modified, preferably linear polyurethane (meth)acrylates (a1) with    terminal, ethylenically unsaturated (meth)acrylic double bonds, and    one or more reactive thinners (a2) with at least two ethylenically    unsaturated (meth)acrylic double bonds, the (meth)acrylic double    bonds of the mixture of (a1) and (a2) corresponding to a bromine    number of 20 to 150 g bromine/100 g solids, and-   B) optionally one or more photoinitiators and optionally one or more    free-radical initiators capable of thermal activation,    -   the terminal, ethylenically unsaturated (meth)acrylic double        bonds of the polyurethane (meth)acrylates being bonded with the        cationically modified polyurethane prepolymer via urethane,        urea, amide or ester groups,    -   and optionally conventional auxiliary substances and additives,        pigments and/or fillers.

DETAILED DESCRIPTION OF THE INVENTION

(Meth)acrylic here is intended to mean acrylic and/or methacrylic.

As component (A), an aqueous, cationic polyurethane dispersionconsisting of e.g. 40 to 85 wt. % of component (a1), calculated as solidresin, and 15 to 60 wt. % of component (a2) is used. The aqueous,cationic polyurethane dispersion (A) has a solids content (polyurethane(meth)acrylate plus reactive thinner) e.g. of 30 to 70 wt. %, preferably40 to 55 wt. %. Its content of terminal, ethylenically unsaturated(meth)acrylic double bonds corresponds to a bromine number of 20 to 150,preferably 20 to 80 g bromine/100 g solids (polyurethane(meth)acrylateplus reactive thinner).

The aqueous dispersion (A) can be produced e.g. by the followingprocess:

A cationically modified urethane prepolymer with terminal NCO groups isfirst produced by reacting

-   i) one or more aliphatic, cycloaliphatic, araliphatic and/or    aromatic polyisocyanates, the aromatic polyisocyanates preferably    having a molecular weight of more than 174,-   ii) one or more higher-molecular-weight polyhydroxyl compound(s)    with a number average molecular weight (Mn) of e.g. 400 to 5000,    preferably 1000 to 2500,-   iii) one or more compound(s) having a group that is cationic by    neutralisation and two groups that are reactive towards isocyanates    and-   iv) optionally one or more low-molecular-weight polyhydroxyl    compounds, e.g. with a number average molecular weight (Mn) of 60 to    less than 400.

The reaction can take place e.g. in a single- or multi-step process,free from solvents or in a polar solvent inert towards NCO groups.

The quantities of components (i) to (iv) in this process are selectede.g. such that the ratio of NCO groups to OH groups is between 4:1 and1.1:1.

The ethylenically unsaturated groups are then added to the free NCOgroups. This takes place e.g. by reacting with compounds (v), which haveone or more ethylenically unsaturated (meth)acrylic groups and one ormore groups that are reactive towards isocyanates, the stoichiometricratios of groups that are reactive towards NCO groups to isocyanategroups being selected such that no free NCO groups remain.

To regulate the functionality (number of ethylenically unsaturated(meth)acrylic double bonds), compounds (vi) having one or more,preferably one group that is reactive towards isocyanates, butcontaining no (meth)acrylic double bonds, can also be incorporated. Theycan contain other ethylenically unsaturated double bonds or can be freefrom them. Following the reaction of components (i) to (iv) for theproduction of a urethane prepolymer, the compounds (vi) can, forexample, be fed into the reaction before, together with or afterreaction with component (v).

The free NCO groups can, however, also be reacted first with compoundswhich, in addition to a group that is reactive towards isocyanates,contain one or more other reactive groups, which in turn can react withgroups of ethylenically unsaturated (meth)acrylic compounds havingcomplementary reactivity, such as e.g. hydroxycarboxylic acid withglycidyl (meth)acrylate. In this way, for example, (meth)acrylic doublebonds bonded to the polyurethane prepolymer via ester groups can beintroduced.

The cationically modified polyurethane (meth)acrylates with terminal,ethylenically unsaturated (meth)acrylic double bonds (a1) have a numberaverage molecular weight Mn of e.g. 800 to 5000 and/or a weight averagemolecular weight Mw of 5000 to 20000, preferably less than 20000. Theiramine value is preferably 5 to 80, particularly preferably 10 to 60.Their content of terminal, ethylenically unsaturated (meth)acrylicdouble bonds is preferably 4 to 80 g bromine/100 g solid resin,particularly preferably 5 to 35 g bromine/100 g solid resin.

The component (a1), obtainable as described above, is diluted with thereactive thinner (a2), at least partially neutralised and transferredinto the aqueous phase. At least 25% of the amino groups are preferablypresent in neutralised form. The neutralising agent can be added beforeor with the water, but it can also be previously added to the water inwhich the polymer is dispersed. It is not necessary to add externalemulsifiers. For the purpose of transferring into the aqueous phase, forexample high-speed disc stirrers, rotor-stator mixers or high-pressurehomogenisers are used. The inert solvent is then distilled off, with theoptional application of a vacuum.

However, the reactive thinner (a2) can also be added subsequently to thedispersion that is already aqueous. In this case the aqueous dispersionis produced as described above, with component (a1) initially not yetbeing diluted with the reactive thinner (a2) or only being diluted withpart of the reactive thinner (a2).

Any organic di- and/or polyisocyanates with aliphatically,cycloaliphatically, araliphatically and/or aromatically bonded freeisocyanate groups having an average of more than one, preferably two,isocyanate groups per molecule are suitable as polyisocyanates (i).Aliphatically, cycloaliphatically and/or araliphatically bonded di-and/or polyisocyanates are preferred. Aromatic diisocyanates preferablyhave a molecular weight of more than 174.

Polyisocyanates containing about 3 to 36, particularly preferably 8 to15, carbon atoms are preferred. Examples of suitable diisocyanates arediphenylmethane diisocyanate and particularly hexamethylenediisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate,dicyclohexylmethane diisocyanate, cyclohexane diisocyanate and mixturesthereof.

The so-called “polyisocyanate lacquer resins”, for example, based onhexamethylene diisocyanate, isophorone diisocyanate and/ordicyclohexylmethane diisocyanate, are very highly suitable, i.e. thederivatives of these diisocyanates having biuret, urethane, uretdioneand/or isocyanurate groups, which are known per se.

Examples of suitable higher-molecular-weight polyhydroxyl compounds (ii)are linear or branched polyols, e.g. with an OH value of 30 to 150.These are preferably saturated polyester and/or polyether diols and/orpolycarbonate diols and/or so-called dimer fatty alcohols and/orpoly(meth)acrylate diols, each with a number-average molecular weight Mnof 400 to 5000, e.g. 500 to 5000, or mixtures thereof.

Suitable linear or branched polyether diols are e.g. poly(oxyethylene)glycols, poly(oxypropylene) glycols and/or poly(oxybutylene) glycols,such as e.g. Terathane® grades from DuPont.

Polyester diols are preferred and can be produced in a known manner byesterification of dicarboxylic acids or their anhydrides with diols. Toproduce branched polyesters, polyols or polycarboxylic acids with higherfunctionality can also be used to a small degree.

Compounds containing two groups reacting with isocyanate, e.g. H-activegroups, and at least one group capable of cation formation areintroduced as suitable compounds (iii). Suitable groups reacting withisocyanate groups are particularly hydroxyl groups. Groups capable ofcation formation are e.g. amino groups. Examples of these compounds arealkyl- or dialkylamino dialcohols with e.g. 1 to 8 C atoms in the alkylportion, the dialcohols optionally being aliphatic, cycloaliphatic oraromatic, aliphatic dialcohols having e.g. 2 to 18 and cycloaliphatice.g. 5 to 14 C atoms, or triamines with a tert. amino group, such ase.g. diethylaminopropanediol, methyldiethanolamine,N,N-diethylaminomethylamine, or ketimine-blocked triamines, such as e.g.ketimine-blocked diethylenetriamine. Aminotriols, such as e.g.triethanolamine, can optionally also be used.

Examples of suitable low-molecular-weight polyhydroxyl compounds (iv)preferably have a number-average molecular weight Mn of 60 to less than500, e.g. of 60 to less than 400 and can contain aliphatic, alicyclicand/or aromatic groups. Suitable low-molecular-weight polyhydroxylcompounds are e.g. diois, triols or polyols, such as ethylene glycol,diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol,1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol, trimethylolpropane,castor oil or hydrogenated castor oil, pentaerythritol,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol F,neopentyl glycol, neopentyl glycol hydroxypivalate, hydroxyethylatedbisphenol A, hydrogenated bisphenol A and mixtures of these polyols.

Suitable compounds (v) having one or more ethylenically unsaturated(meth)acrylic groups and one or more groups that are reactive towardsisocyanates contain hydroxyl, amino and/or amide groups as reactivegroups. (Meth)acrylic double bonds bonded via urethane groups areintroduced into the polyurethane prepolymer via thehydroxyl-group-containing compounds (v); compounds (v) containing aminogroups lead to bonding via urea groups; compounds (v) containing amidegroups lead to bonding via “amide groups”, with α-ketourea groupsparticularly being formed.

Examples of hydroxyl-group-containing compounds (v) are hydroxy(meth)acrylates, such as e.g. hydroxyl-group-containing esters ofacrylic acid and/or methacrylic acid with 2 to 12, preferably 2 to 6 Catoms in the hydroxyalkyl radical, such as e.g. 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl(meth)acrylate and the corresponding isomeric compounds2-hydroxy-1-methylethyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl(meth)acrylate and others; reaction products of (meth)acrylic acid withpolyols, such as e.g. glycerol diacrylate, trimethylolpropanediacrylate, pentaerythritol triacrylate; pre-adducts of glycidylnethacrylate and hydroxycarboxylic acids, such as e.g. glycolic acid;reaction products of hydroxy (meth)acrylates with ε-caprolactone;reaction products of (meth)acrylic acid with the glycidyl ester of acarboxylic acid having a tertiary α-C atom, such as e.g. Cardura® fromShell.

Examples of amino-group-containing compounds are amino (meth)acrylates,such as e.g. tert.-butylaminoethyl (meth)acrylate, (meth)acrylicacid-β-ureidoethyl ester or reaction products of (meth)acrylic acidchloride and diamines.

Examples of compounds with amide groups are (meth)acrylamide, N-methylol(meth)acrylamide and isobutylmethylol (meth)acrylamide. The compounds(v) can be used individually or as mixtures.

Suitable compounds (vi) for regulating the functionality are e.g. higherglycol ethers and/or fatty alcohols and/or fatty amines. One or morealiphatic C₄–C₃₆ alcohols and/or amines can be used, for example, whichare generally then reacted with complete consumption of their OH, NH orNH₂ groups. Fatty amines and/or fatty alcohols with more than 12 Cgroups are preferred. Examples are lauryl alcohol, stearyl alcohol andthe corresponding amines.

Ethylenically unsaturated, particularly low-molecular-weight andoligomolecular compounds, are suitable as reactive thinners (a2). Unlikethe polyurethane (meth)acrylate component (a1), the reactive thinners donot usually have any cationic modifications. The low-molecular-weightand/or oligomolecular reactive thinners can, for example, havecalculated molecular weights in the order of magnitude of up to 10000,e.g. 100 to 10000. Suitable reactive thinners are e.g. di- andpoly(meth)acrylates of glycols with 2 to 6 C atoms and polyols with 3 to4 OH groups and 3 to 6 C atoms, such as ethylene glycol diacrylate,1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanedioldiacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate and corresponding methacrylates, and alsodi(meth)acrylates of polyether glycols of glycol, 1,3-propanediol,1,4-butanediol, tetraethoxylated trimethylolpropane triacrylate and/oroligourethane (meth)acrylates with 2 to 6 ethylenically unsaturateddouble bonds. Mixtures can also be used.

Conventional inorganic acids are suitable as neutralising agents, suchas e.g. hydrochloric acid, sulfuric acid, sulfurous acid, phosphoricacid and chromic acid, but organic acids are preferred, particularlymonocarboxylic acids, such as e.g. formic acid, acetic acid, propionicacid and particularly hydroxycarboxylic acids, such as e.g. lactic acid,glycolic acid, diglycolic acid, malic acid, citric acid, mandelic acid,tartaric acid, hydroxypropionic acid and dimethylolpropionic acid.Mixtures of such neutralising agents can also be used.

The stability of the dispersion can be influenced in the way that isfamiliar to the person skilled in the art by the selection of theneutralising agent. The quantity of neutralising agent is generallyselected such that at least 25% of the ionic groups are present in saltform.

The electrophoretic lacquers according to the invention can optionallycontain one or more photoinitiators and/or optionally one or morefree-radical initiators capable of thermal activation. Theelectrophoretic lacquers according to the invention are preferably curedin the presence of photoinitiators, but the curing can also take placewithout photoinitiators.

Any initiators that are conventional for free-radically curing systemscan be used as suitable photoinitiators (B), e.g. those absorbing in thewavelength range of 190 to 600 nm.

Examples are acetophenone and derivatives, benzophenone and derivatives,benzil, Michler's ketone, thioxanthone and derivatives, anthrone,anthraquinone and derivatives; benzoin and derivatives, benzoin etherand derivatives, dialkoxy acetophenones, acyloxime esters, benzilketals, hydroxyalkylphenones; organophosphorus compounds, such as e.g.acylphosphine oxides; haloketones. The photoinitiators are used inconventional quantities, e.g. of 0.1 to 20 wt. %, preferably 0.1 to 5wt. %, based on the sum of polymers that can be polymerised by freeradicals (a1) and reactive thinner (a2). The photoinitiators can be usedindividually or in combination.

In addition to the photoinitiators mentioned, so-called photoactivators,such as e.g. tertiary amines, can be added. Synergistic effects aresometimes achieved with combinations of this type.

In a less preferred embodiment, the curing is performed withoutphotoinitiators.

The aqueous electrophoretic lacquer capable of being depositedcataphoretically according to the invention can contain conventionallacquer auxiliary substances and additives in addition to the aqueousdispersion (A) and the photoinitiator (B), such as e.g. biocides, lightstabilisers, flow promoters and optionally pigments and/or fillers.

The pigments and fillers in this case are the conventional fillers thatcan be used in the lacquer industry and inorganic or organic colouringand/or special-effect pigments and anticorrosive pigments. Examples ofinorganic and organic colouring pigments are titanium dioxide,micronised titanium dioxide, zinc sulfide, lithopone, lead carbonate,lead sulfate, tin oxide, antimony oxide, iron oxides, chrome yellow,nickel titanium yellow, chrome orange, molybdenum red, mineral violet,ultramarine violet, ultramarine blue, cobalt blue, chrome oxide green,carbon black, azo, phthalocyanine, quinacridone, perylene, perinone,anthraquinone, thioindigo and diketopyrrolopyrrole pigments. Examples ofspecial-effect pigments are metallic pigments, e.g. of aluminium, copperor other metals; interference pigments, such as e.g. metal oxide-coatedmetallic pigments or metal oxide-coated mica; pearlescent pigments andoptically variable pigments (OVP).

Examples of fillers are calcium carbonate, barium sulfate, talcum,silicon dioxide, aluminium silicates, magnesium silicates, mica,aluminium hydroxide and silicas. The fillers can also be modified(coated) with organic compounds, which can also contain UV-curablegroups. Examples of these modified fillers are coated micronisedaluminium oxide or coated micronised silicon dioxide.

The aqueous electrophoretic lacquer capable of being depositedcataphoretically according to the invention can also contain otherhydrophilic and/or hydrophobic polymers with or without reactive groups,such as e.g. hydroxyl, amino and other groups or mixtures of thesepolymers, which can optionally also be thermally crosslinked.

Examples of these polymers are saturated or unsaturated acrylic orpolyester resins, acrylate-modified acrylic or polyester resins, epoxyresins, aminoplastic resins, phenolic resins and blockedpolyisocyanates.

The electrophoretic lacquer is produced by mixing components (A) and (B)and optionally other lacquer auxiliary substances and additives, e.g.with the aid of conventional mixers such as e.g. (high-speed) stirrers,static mixers, rotor/stator mixers and other homogenisers.

The pigments and/or fillers that are optionally incorporated areprocessed in a portion of component (A) or a special paste resin in aknown manner by conventional dispersing processes to form a pigmentpaste, which is mixed into components (A) and (B) as described above.

In the case of the initial filling of an electrophoretic lacquer bath,the electrophoretic lacquer produced in this way can optionally beadjusted to the desired bath MEQ value with farther neutralising agentand adjusted to the desired bath solids with deionised water. The MEQvalue is a measure of the content of neutralising agent in a water-basedlacquer. It is defined as the quantity of milliequivalents of theneutralising agent based on 100 g of solids.

In the case of post-compensation, the amino groups of component (A) canbe only partly neutralised to compensate for the neutralising agentreleased during deposition.

The bath MEQ value is e.g. 15 to 70, preferably 20 to 45milliequivalents of neutralising agent, e.g. acid/100 g solids, and thebath solids content is 5 to 25%, preferably 8 to 18%.

The electrophoretic lacquer according to the invention is suitable forcoating workpieces with an electrically conductive surface, e.g. metal,electrically conductive (e.g. metallised) plastic, electricallyconductive wood or electrically conductive coatings (e.g. lacquers), forexample for the priming and/or one-coat lacquering of domestic andelectrical appliances, steel furniture, structural components andagricultural machinery and car accessories as well as car bodies,particularly for the clear lacquer coating of aluminium, such as e.g. ofpretreated aluminium profiles, and for the sealing of conductivecoatings (e.g. electrophoretic lacquer coatings).

The coatings produced with the electrophoretic lacquer according to theinvention can, however, also be provided with other lacquer coatings inthe conventional way to form a multi-coat construction.

In a suitable coating plant, the substrate to be coated is immersed inthe electrophoretic lacquer bath filled with the electrophoretic lacqueraccording to the invention and is connected as the cathode in a DCcircuit opposite a counter-electrode. These coating plants are known tothe person skilled in the art and described e.g. in “Glasurithandbuch”1984, pages 374 to 384.

A film of up to film thicknesses of 60 μm, preferably between 10 and 50μm, is deposited, e.g. at a coating temperature of 15 to 30° C.,preferably 18 to 22° C. with a DC voltage of 50 to 500 volts, preferably100 to 300 volts for a coating period of 1 to 5 minutes, preferably 2 to3 minutes.

The deposition can take place both intermittently and continuously.

The deposited film is freed from any adhering bath material by rinsingwith ultrafiltrate and/or deionised water, and freed from any dropletsof water that are clinging on by blowing off in an optionally heated airstream or by supported evaporation with an IR radiator, and exposed tohigh-energy radiation, such as electron beam radiation, preferably UVradiation, for the purpose of curing.

For the radiation curing of the coating compound according to theinvention, any known sources of radiation can be used. Ad radiationsources, for example, with emissions in the wavelength range of 180 to420 nm, particularly 200 to 400 nm, are suitable. Examples of these UVradiation sources are high-pressure, medium-pressure and low-pressuremercury vapour radiators, gas discharge tubes such as e.g. xenon vapour,xenon/mercury vapour, (low-pressure) germanium vapour lamps, UVlight-emitting diodes and UV light-emitting lasers. The irradiation canalso take place with pulsed radiation, e.g. with pulsed UV radiation.So-called high-energy electron flash generators (UV flash lamps), asdescribed e.g. in WO-A-94 11 123 or EP-A-525 340 and commerciallyavailable, are particularly preferably used as sources of radiation.

The irradiation period is in the range of e.g. 1 millisecond to 30minutes, depending on the lacquer system and source of radiation. Thedistance from the source of radiation to the substrate surface to beirradiated is e.g. 2 to 50 cm, preferably 5 to 10 cm. The irradiationperiod is selected such that, as far as possible, a complete cure isachieved, i.e. the formation of the required technological properties isguaranteed. For this purpose, the substrate surface to be irradiated canbe passed in front of the source of radiation several times, or, withthe preferred use of UV flash lamps, the irradiation can take place witha multiple flash discharge. The flashes can be triggered e.g. every 4seconds, since the UV flash lamps do not require any bum-in period.

To avoid any radiation leakage, the sources of radiation are shieldedagainst the environment.

In addition, it is possible to apply thermal activation to crosslink thecoating compounds according to the invention, in order to cure areasthat can only be exposed to the radiation inadequately.

For this purpose it can be advantageous to incorporate conventionalfree-radical initiators that are capable of thermal activation, so that,after the irradiation or at the same time as the irradiation, athermally activated free-radical polymerisation takes place.

Examples of free-radical initiators that are capable of thermalactivation are organic peroxides, organic azo compounds or C—C-splittinginitiators, such as e.g. dialkyl peroxides, peroxocarboxylic acids,peroxide carbonates, peroxide esters, hydroperoxides, ketone peroxides,azodinitriles or benzopinacole silyl ethers.

The free-radical initiators that are capable of thermal activation canalso be used in a mixture. The preferred amounts are 0.1 to 5 wt. %,based on the sum of components (a1) and (a2), which can be polymerisedby free radicals.

The films deposited with the aqueous electrophoretic lacquer accordingto the invention and cured are distinguished by high gloss, very goodadhesion and good edge coverage. In addition to high scratch resistance,they exhibit excellent resistance to acids, alkalis and solvents and toindustrial atmospheres, particularly acidic waste gases, such as sulfurdioxide, particularly in a damp atmosphere, which can be proved e.g. bythe Kesternich test (DIN or ISO 3231).

Other advantages are a fully automatic process, high applicationefficiency, low-waste implementation as a result of closed circuits,low-solvent or solvent-free operation, extremely short curing times andlow thermal stress to the substrates to be lacquered.

EXAMPLE 1

400.2 g of acetone, 133.0 g of diethylaminopropanediol and 849.8 g of apolyester diol consisting of neopentyl glycol, adipic acid andisophthalic acid (OH value=106 mg KOH/g solid resin) are initiallyplaced in a reaction vessel with a stirrer, thermometer and refluxcondenser and reacted with 510.4 g of isophorone diisocyanate at 60° C.,until an NCO content of 1.7% is reached.

106.6 g of hydroxyethyl acrylate are added to the NCO prepolymersolution thus obtained and stirred at 60° C. until the NCO content hasfallen below 0.2%.

551.0 g of the polyurethane acrylate thus obtained are diluted with188.9 g of trimethylolpropane triacrylate, neutralised with 58.7 g of50% formic acid and, after stirring for 1 hour at 60° C., dispersed in1194.6 g of deionised water. The acetone is removed by vacuumdistillation.

The dispersion thus obtained has a solids content (30 minutes 150° C.)of 35% and a content of double bonds of 63 g bromine/100 g solids.

9.0 parts by weight of 2-hydroxy-2-methyl-1-phenylpropanone aredispersed in 857.1 parts by weight of the dispersion. This is thendiluted with 1133.9 parts by weight of deionised water.

In the electrophoretic lacquer bath thus obtained, zinc phosphated steelplates are coated at a bath temperature of 25° C. for 2 minutes with aseries resistor of 200 ohms with 100 to 200 volts.

The deposited film is rinsed with water and freed from any waterdroplets that are clinging on by blowing off with compressed air. It isthen cured on a belt conveyor with 2 UV radiators (80 W/cm) at a beltspeed of 3×3 m. The cured films have a film thickness of 15 to 30 μm,are high-gloss and display very good flow.

Various tests were performed on the cured films with a 20 μm filmthickness; the results for Erichsen indentation, crosshatch adhesiontest and chemical resistance are listed below.

Erichsen indentation according to EN-ISO 1520: 9–10 mm Crosshatchaccording to EN-ISO 2409: no detachment

Chemical resistance of vehicle lacquers based on VDA test specification621-412:

-   10 minutes xylene no swelling or detachment-   60 seconds acetone no swelling or detachment.

1. An aqueous electrophoretic lacquer capable of being depositedcataphoretically having a solids content of 30 to 70 wt. % comprising anaqueous dispersion A) comprising 40 to 85 wt. % of component a1)comprising at least one cationically modified polyurethane(meth)acrylate having terminal, ethylenically unsaturated (meth)acrylatedouble bonds and 15 to 60 wt. % of component a2) comprising at least onereactive thinner having at least two ethylenically unsaturated(meth)acrylic double bonds; wherein the polyurethane (meth)acrylatecomprises a cationically modified urethane prepolymer having terminalNCO groups bonded via groups selected from the group consisting ofurethane, urea, amide and ester groups to the terminal ethylenicallyunsaturated (meth)acrylic double bonds to form the polyurethane(methacrylate); and wherein the (meth)acrylic double bonds of themixture of component a1) and component a2) correspond to a brominenumber of 20 to 150 g bromine/100 g solids and wherein the urethaneprepolymer is the reaction product of i) at least one isocyanateselected from the group consisting of aliphatic polyisocyanate,cycloaliphatic polyisocyanates, araliphatic polyisocyanates, aromaticpolyisocyanates and any mixtures thereof, said polyisocyanates having amolecular weight of more than 174; ii) at least one polyhydroxylcompound with a number average molecular weight of Mn of 400 to 5000,iii) at least one compound having a group that is cationic byneutralization and two groups that are reactive with isocyanates, andiv) optionally, at least one polyhydroxyl compound having a numberaverage molecular weight Mn of 60 to less than
 400. 2. Theelectrophoretic lacquer according to claim 1 further comprising at leastone photo-initiator, at least one free-radical initiator capable ofthermal activation, conventional auxiliary substances, additives,pigments and fillers.
 3. The electrophoretic lacquer according to claim1, wherein the bromine number of component a1) is 4 to 80 g bromine/100g solid resin.
 4. An The electrophoretic lacquer capable of beingdeposited cataphoretically having a solids content of 30 to 70 wt. %comprising an aqueous dispersion A) comprising 40 to 85 wt. % ofcomponent a1) comprising at least one cationically modified,polyurethane (meth)acrylate having terminal, ethylenically unsaturated(meth)acrylate double bonds and 15 to 60 wt. % of component a2), areactive thinner having at least two ethylenically unsaturated(meth)acrylic double bonds; wherein the (meth)acrylic double bonds ofthe mixture of component a1) and component a2) correspond to a brominenumber of 20 to 150 g bromine/100 g solids, and; wherein thepolyurethane (meth)acrylate is the reaction product of a urethaneprepolymer with terminal NCO groups and at least one compound having atleast one ethylenically unsaturated (meth)acrylic group and having atleast one group that is reactive with isocyanate and optionally, atleast one compound having at least one group that is reactive withisocyanate and having no (meth)acrylic double bonds: wherein theurethane prepolymer is the reaction product of i) at least oneisocyanate selected from the group consisting of aliphaticpolyisocyanate, cycloaliphatic polyisocyanates, araliphaticpolyisocyanates, aromatic polyisocyanates and any mixtures thereof, saidpolyisocyanates having a molecular weight of more than 174; ii) at leastone polyhydroxyl compound with a number average molecular weight of Mnof 400 to 5000, iii) at least one compound having a group that iscationic by neutralization and two groups that are reactive withisocyanates, and iv) at least one polyhydroxyl compound having a numberaverage molecular weight Mn of 60 to less than 400; and wherein the atleast one compound having at least one ethylencially unsaturated(meth)acrylic group and at least one group reactive with isocyanate isselected from the group consisting of hydroxyalkyl (meth)acrylates,aminoalkyl(meth)acrylates, (meth)acrylamides, compounds having one groupreactive with isocyanate and one group suitable for the addition of a(meth)acrylic ester group and subsequent addition of the (meth)acrylicester group and mixtures of any of the above; and wherein component a1),polyurethane (meth)acrylate and component a2) reactive thinner are atleast partially neutralized and formed into the aqueous dispersion.
 5. Aprocess for forming an aqueous dispersion A) comprising 40 to 85 wt. %of component a1) comprising at least one cationically modifiedpolyurethane (meth)acrylate having terminal, ethylenically unsaturated(meth)acrylate double bonds and 15 to 60 wt. % of component a2)comprising at least one reactive thinner having at least twoethylencially unsaturated (meth)acrylic double bonds useful forelectrophoretic lacquers, the process comprising the steps of forming aurethane prepolymer with terminal NCO groups and reacting the urethaneprepolymer with at least one compound having at least one ethylenicallyunsaturated (meth)acrylic group reactive with isocyanate and optionally,with at least one compound having at least one group reactive withisocyanate and having no (meth)acrylic double bonds to form apolyurethane (meth)acrylate; and mixing the resulting polyurethane(meth)acrylate with at least one reactive thinner having at least twoethylenically unsaturated double bonds and subsequently, at leastpartially neutralizing the resulting mixture and adding aqueous fluid toform the aqueous dispersion; wherein the (meth)acrylic double bonds ofthe mixture of component a1) and component a2) correspond to a brominenumber of 20 to 150 g bromine/100 g solids, wherein the urethaneprepolymer having terminal NCO groups is the reaction product of: i) atleast one isocyanate selected from the group consisting of aliphaticpolyisocyanate, cycloaliphatic polyisocyanates, araliphaticpolyisocyanates, aromatic polyisocyanates and any mixtures thereof, saidpolyisocyanates having a molecular weight of more than 174; ii) at leastone polyhydroxyl compound with a number average molecular weight of Mnof 400 to 5000, iii) at least one compound having a group that iscationic by neutralization and two groups that are reactive withisocyanates, and iv) optionally, at least one polyhydroxyl compoundhaving a number average molecular weight Mn of 60 to less than 400; andwherein the at least one compound having at least one ethylenicallyunsaturated (meth)acrylic group and at least one group reactive withisocyanate is selected from the group consisting of hydroxyalkyl(meth)acrylates, aminoalkyl(meth)acrylates, (meth)acrylamides, compoundshaving one group reactive with isocyanate and one group suitable for theaddition of a (meth)acrylic ester group and subsequent addition of the(meth)acrylic ester group and mixtures of any of the above.
 6. Processfor electrophoretic lacquering of electrically conductive substrateswhich comprises the steps of immersing the electrically conductivesubstrate in an aqueous electrophoretic lacquer and applying a coatingthereon whereby the substrate is connected as a cathode and curing thecoating on the substrate with high-energy radiation; wherein theelectrophoretic lacquer comprises the composition of claim
 1. 7. Theprocess of claim 6 wherein the coating is additionally cured by thermalmeans.
 8. An electrically conductive substrate coated according to theprocess of claim
 6. 9. An electrically conductive substrate coatedaccording to the process of claim 6 having in addition a multi-coatfinish thereon.